The invention relates to a method and apparatus for generating a twelve-lead electrocardiogram (ECG) from a plurality of fewer than ten electrodes for attachment to a patient in the standard ten-electrode, twelve-lead ECG positions.
A standard, resting ECG is acquired with ten electrodes. Four of the ten electrodes are placed on the patient's limbs. Six of the ten electrodes are attached to the patient's chest over the heart. The signals acquired by the ten electrodes are amplified and processed to generate twelve channels of ECG data. The twelve channels or leads are generally split into two groups—the frontal plane leads (I, II, III, aVR, aVL, aVF) and the horizontal plane leads (V1, V2, V3, V4, V5, V6).
A standard, resting ECG has several limitations. First, the six electrodes attached to the patient's chest inhibit the clinicians' access to the patient's chest. Second, clinicians may not be able to attach all six chest electrodes due to wounds or bandages on the patient's chest. The electrodes, leadwires, and amplifiers necessary to acquire twelve channels of ECG data increase the cost of the ECG machine. Fourth, the amount of data representing twelve channels of ECG generally exceeds the maximum amount or bandwidth that typical telemetry units are able to transmit.
U.S. Pat. No. 4,850,370 provides a solution to some of the above-described limitations. The '370 Patent discloses a method of sensing and analyzing the electrical activity of the human heart by sensing the voltage signals generated by the heart between four electrodes located at key positions on the surface of the subject's body. A signal processing means produces electrocardiographic signals corresponding to the lead signals of a twelve-lead electrocardiogram.
FIG. 3 illustrates the electrode placement for the method of generating a twelve-lead ECG from four electrodes as disclosed in the '370 Patent. The four electrodes are designated as E, A, S, and I (hereinafter referred to collectively as the “EASI electrodes”). The E electrode is located at the front midline over the lower end of the sternum. The A electrode is located at the left mid-axillary line. The S electrode is located at the front midline over the upper end of the sternum. The I electrode is located at the right mid-axillary line.
The EASI electrodes are coupled to a signal processor (not shown) having a first stage and a second stage. The first stage of the signal processor does not generate the twelve-lead ECG, but rather generates xyz vectorcardiographic signals. The twelve-lead ECG is then derived from the xyz vectorcardiographic signals in the second stage of the signal processor. As a result of the two stage signal processing, each of the twelve leads generated from the EASI electrodes are mathematically generated. In other words, none of the leads are the same as the leads that would be generated from the electrical signals of a standard ten-electrode, twelve-lead ECG.
The method of the '370 Patent has several limitations. First, the four electrodes are placed in non-standard positions, i.e. positions different from the electrode positions for a standard ten-electrode, twelve-lead ECG. This requires clinicians to be trained specifically for the method of the '370 Patent. Second, twelve leads of ECG data are generated, but all twelve leads are generated mathematically. None of the twelve leads in the method of the '370 Patent are the same as the leads that would be generated from a standard ten-electrode, twelve-lead ECG. Rather, all twelve leads are mere approximations of the leads of a standard ten-electrode, twelve-lead ECG. Third, two of the four electrodes are placed directly over the sternum. The sternum is cracked for all open chest surgeries in a procedure called sternotomy. Thus, the clinician may not be able to attach the two electrodes directly over the sternum due to sternotomy wounds and bandages.